Electrochemical cell including electrolyte containing bis(oxalate)borate salt

ABSTRACT

An electrochemical cell includes a cathode containing an aluminum current collector, a positive lead coupled to the cathode current collector an anode, and an electrolyte including from greater than 0.075 M to less than 0.2 M of a bis(oxalate)borate salt and a second lithium salt. The positive lead may include a metal selected from aluminum, titanium, and steel. The anode may include lithium, graphite, and a lithiated metal oxide. The aluminum current collector has an aluminum surface having at least one dimension greater than 1 millimeter.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation application of and claims priority toU.S. Ser. No. 12/264,984, filed on Nov. 5, 2008, now U.S. Pat. No.8,309,255, which in turn is a continuation of and claims priority toU.S. Ser. No. 10/800,905, filed on Mar. 15, 2004, now U.S. Pat. No.7,459,237. Both are hereby incorporated by reference.

TECHNICAL FIELD

The invention relates to non-aqueous electrochemical cells.

BACKGROUND

Batteries or electrochemical cells are commonly used electrical energysources. A battery contains a negative electrode, typically called theanode, and a positive electrode, typically called the cathode. The anodecontains an active material that can be oxidized; the cathode containsor consumes an active material that can be reduced. The anode activematerial is capable of reducing the cathode active material.

When a battery is used as an electrical energy source in a device,electrical contact is made to the anode and the cathode, allowingelectrons to flow through the device and permitting the respectiveoxidation and reduction reactions to occur to provide electrical power.An electrolyte in contact with the anode and the cathode contains ionsthat flow through the separator between the electrodes to maintaincharge balance throughout the battery during discharge.

SUMMARY

In one aspect, the invention features an electrochemical cell includinga cathode containing MnO₂, an anode containing lithium, and anelectrolyte containing a bis(oxalato)borate salt. The cell includes analuminum surface in electrical contact with a second metal surface thatis different from the aluminum surface.

In certain embodiments, the cell includes a metal as a constructionmaterial. For example, the metal can be used to construct a cellcontainer (or can), or a current collector for the positive electrode.Sometimes, the metal can corrode because the electrode potential of themetal is lower than the normal operating potential of the positiveelectrode of the cell. When the metal is coupled with different metalsin the environment of an electrochemical cell, the metal can also besusceptible to corrosion. Corrosion can increase the internal impedanceof a cell, leading to capacity loss and to a decrease in specificenergy. Corrosion can also limit the choice of metals available as aconstruction material.

The bis(oxalato)borate salt additive can help to suppress corrosion ofmetal (e.g., aluminum) parts that contact the electrolyte of the cell.

In another aspect, the invention features a primary electrochemical cellhaving a cathode containing an aluminum current collector, an anode, andan electrolyte containing a bis(oxalato)borate salt. The electrolytealso includes a second salt that is a lithium salt.

In another aspect, the invention features an electrochemical cell havinga cathode containing MnO₂, an anode containing lithium, an aluminumsurface, and an electrolyte containing a bis(oxalato)borate salt at aconcentration that is equal to or less than about 0.2 M.

In another aspect, the invention features a primary electrochemical cellhaving a cathode containing MnO₂, an anode containing lithium, and anelectrolyte containing a bis(oxalato)borate salt. The cell includes analuminum surface in contact with a second metal surface that isdifferent from the aluminum surface.

In another aspect, the invention features a primary electrochemical cellhaving a cathode containing MnO₂, an anode containing lithium, and anelectrolyte containing a bis(oxalato)borate salt. The cell includes twopieces of aluminum that are in electrical contact with each other.

In another aspect, the invention features a primary electrochemical cellhaving a cathode containing MnO₂, an anode containing lithium, and anelectrolyte containing a bis(oxalato)borate salt at a concentration thatis equal to or less than about 0.2 M.

In another aspect, the invention features an electrochemical cell havinga cathode containing MnO₂, an anode containing lithium, and anelectrolyte containing a bis(oxalato)borate salt at a concentration ofless than about 0.2 M.

In another aspect, the invention features a method of inhibitingaluminum corrosion in a primary electrochemical cell. The methodincludes adding a bis(oxalato)borate salt to an electrolyte and placingthe electrolyte, an anode containing lithium, and a cathode containingan aluminum current collector into a cell case to form the cell.

Aspects of the invention may include one or more of the followingfeatures.

In some embodiments, the cell is a primary electrochemical cell. Inother embodiments, the cell is a secondary electrochemical cell.

The bis(oxalato)borate salt can be an ammonium salt (e.g.,tetraethylammonium-bis(oxalato)borate,butylammonium-bis(oxalato)borate), lithium-bis(oxalato)borate,potassium-bis(oxalato)borate, or sodium-bis(oxalato)borate. In someembodiments, the electrolyte can contain the bis(oxalato)borate salt ata concentration that is equal to or less than about 0.2 M (e.g., lessthan about 0.15 M, less than about 0.1 M, less than about 0.05 M, lessthan about 0.025 M). In certain embodiments, the electrolyte can containa second salt (e.g., a lithium salt, such as lithiumtrifluoromethanesulfonate (LiTFS), lithium trifluoromethanesulfonimide(LiTFSI), or a combination thereof). The electrolyte can contain a thirdsalt (e.g., a lithium salt). In some embodiments, the electrolyte cancontain a fourth salt (e.g., a lithium salt).

The aluminum surface can be a portion of an object having at least onedimension greater than 0.5 millimeter (e.g., greater than onemillimeter, greater than two millimeters). The cell can have a case thatincludes aluminum. The case can be essentially of aluminum. The secondmetal surface that is in electrical contact with the aluminum surfacecan be a steel surface, an aluminum or aluminum alloy surface, or anickel surface. In some embodiments, the cell can include a cathodecurrent collector made of aluminum.

The cathode can include at least one of the following: MnO₂, V₂O₅, CoF₃,MoS₂, FeS₂, SOCl₂, MoO₃, sulfur, (C₆H₅N)_(n) (where n is at least two),(S₃N₂)_(n) (where n is at least two), or a fluorocarbon. The anode caninclude lithium.

In some embodiments, the method further includes adding a second salt(e.g., a lithium salt) to the electrolyte. The method can include addinga third salt (e.g., a lithium salt) to the electrolyte and in someembodiments, the method includes adding a fourth salt (e.g., a lithiumsalt) to the electrolyte.

Other aspects, features, and advantages are in the description,drawings, and claims.

DESCRIPTION OF DRAWINGS

FIG. 1 is a sectional view of a nonaqueous electrochemical cell.

FIG. 2 is a graph showing current density versus time of aluminumelectrodes at 3.6 V and at 3.8 V in an electrolyte containing 0.01 Mlithium-bis(oxalato)borate.

FIG. 3 is a graph showing current density versus time of aluminumelectrodes at 3.6 V, 3.8 V, 4.0 V, and 4.2 V in an electrolytecontaining 0.03 M lithium-bis(oxalato)borate.

FIG. 4 is a graph showing current density versus time of aluminumelectrodes at 3.8 V, 4.0 V, 4.2 V, and 4.5 V in an electrolytecontaining 0.05 M lithium-bis(oxalato)borate.

FIG. 5 is a graph showing current density versus time of aluminumelectrodes at 3.8 V, 4.0 V, 4.2 V, and 4.5 V in an electrolytecontaining 0.1 M lithium-bis(oxalato)borate.

FIG. 6 is a graph showing current density versus potential of aluminumelectrodes in electrolytes containing different concentrations (0.0 M,0.03 M, 0.05 M, 0.1 M, and 0.2 M) of lithium-bis(oxalato)borate.

DETAILED DESCRIPTION

Referring to FIG. 1, an electrochemical cell 10 includes an anode 12 inelectrical contact with a negative lead 14, a cathode 16 in electricalcontact with a positive lead 18, a separator 20 and an electrolyticsolution. Anode 12, cathode 16, separator 20 and the electrolyticsolution are contained within a case 22. The electrolytic solutionincludes a solvent system and a salt that is at least partiallydissolved in the solvent system. Electrochemical cell 10 furtherincludes a cap 24 and an annular insulating gasket 26, as well as asafety valve 28.

The electrolytic solution or electrolyte can be in liquid, solid or gel(polymer) form. The electrolyte can contain an organic solvent such aspropylene carbonate (PC), ethylene carbonate (EC), dimethoxyethane(DME), butylene carbonate (BC), dioxolane (DO), tetrahydrofuran (THF),acetonitrile (CH₃CN), gamma-butyrolactone, diethyl carbonate (DEC),dimethyl carbonate (DMC), ethyl methyl carbonate (EMC),dimethylsulfoxide (DMSO), methyl acetate (MA), methyl formiate (MF),sulfolane, or combinations thereof. The electrolyte can alternativelycontain an inorganic solvent such as SO₂ or SOCl₂. The electrolyte alsocan contain a lithium salt, such as lithium trifluoromethanesulfonate(LiTFS) or lithium trifluoromethanesulfonimide (LiTFSI), or acombination thereof. Additional lithium salts that can be included arelisted in U.S. Pat. No. 5,595,841, which is hereby incorporated byreference in its entirety. In some embodiments, the electrolyte maycontain LiPF₆; in other embodiments, the electrolyte is essentially freeof LiPF₆.

In preferred embodiments, the electrolyte also contains abis(oxalato)borate salt, which inhibits corrosion in the cell. Examplesof bis(oxalato)borate salts include lithium-bis(oxalato)borate (LiBOB),sodium-bis(oxalato)borate, potassium-bis(oxalato)borate, and ammoniumsalts such as tetraethylammonium-bis(oxalato)borate andbutylammonium-bis(oxalato)borate. The bis(oxalato)borate salt can beincluded in the electrolyte at concentrations of, for example, fromabout 0.01 M to about 0.2 M.

In some embodiments, the electrolyte can include the bis(oxalato)boratesalt at a concentration that is equal to or greater than about 0.005 M(e.g., greater than about 0.01 M, greater than about 0.025 M, greaterthan about 0.05 M, greater than about 0.075 M, greater than about 0.1 M,greater than about 0.125 M, greater than about 0.15 M, greater thanabout 0.175 M). Alternatively or in addition, the electrolyte caninclude the bis(oxalato)borate salt at a concentration that is equal toor less than about 0.2 M (e.g., less than about 0.175 M, less than about0.15 M, less than about 0.125 M, less than about 0.1 M, less than about0.075 M, less than about 0.05 M, less than about 0.025 M, less thanabout 0.01 M, less than about 0.005 M). An effective amount ofbis(oxalato)borate salt to reduce, e.g., inhibit, corrosion to a desiredlevel in the cell can be determined experimentally, e.g., using cyclicvoltammetry.

The electrolyte can include only one salt (i.e., the bis(oxalato)boratesalt), or it can include more than one salt. In some embodiments, theelectrolyte includes, for example, two salts, three salts, or foursalts. One or more of the salts can be, for example, a lithium salt.

In some embodiments, electrochemical cell 10 includes an electrolyteformed of a mixture of solvents having DME and PC, and a salt mixture ofLiTFS and LiTFSI. The concentration of DME in the mixture of solventscan range from about 30 percent to about 85 percent by weight. Theconcentration of DME in the mixture of solvents can be equal to orgreater than about 30 percent, 35 percent, 40 percent, 45 percent, 50percent, 55 percent, 60 percent, 65 percent, 70 percent, 75 percent, or80 percent by weight; and/or equal to or less than about 85 percent, 80percent, 75 percent, 70 percent, 65 percent, 60 percent, 55 percent, 50percent, 45 percent, 40 percent, or 35 percent by weight. Theconcentration of PC in the mixture of solvents can be equal to 100percent minus the concentration of DME. For example, if theconcentration of DME in the mixture of solvents is 75 percent by weight,then the concentration of PC in the mixture of solvents is 25 percent byweight. If the concentration of DME in the mixture of solvents is 50-75percent by weight, then the concentration of PC in the mixture ofsolvents is 25-50 percent by weight.

For the LiTFS and LiTFSI salt mixture, the total concentration of saltin the mixture of solvents can range from about 0.4 M to about 1.2 M.The total concentration of LiTFS and LiTFSI in the mixture of solventscan be equal to or greater than about 0.40 M, 0.45 M, 0.50 M, 0.55 M,0.60 M, 0.65 M, 0.70 M, 0.75 M, 0.80 M, 0.85 M, 0.90 M, 0.95 M, 1.00 M,1.05 M, 1.10 M, or 1.15 M; and/or equal to or less than about 1.2 M,1.15 M, 1.10 M, 1.05 M, 1.00 M, 0.95 M, 0.90 M, 0.85 M, 0.80 M, 0.75 M,0.70 M, 0.65 M, 0.60 M, 0.55 M, 0.50 M, or 0.45 M. Of the totalconcentration of salt, the concentration of LiTFS in the mixture ofsolvents can be (in mole fraction) equal to or greater than fivepercent, ten percent, 15 percent, 20 percent, 25 percent, 30 percent, 35percent, 40 percent, 45 percent, 50 percent, 55 percent, 60 percent, 65percent, 70 percent, 75 percent, 80 percent, 85 percent, 90 percent, or95 percent; and/or equal to or less than 100 percent, 95 percent, 90percent, 85 percent, 80 percent, 75 percent, 70 percent, 65 percent, 60percent, 55 percent, 50 percent, 45 percent, 40 percent, 35 percent, 30percent, 25 percent, 20 percent, 15 percent, ten percent, or fivepercent. The concentration of LiTFSI in the mixture of solvents can beequal to 100 percent minus the concentration of LiTFS in the mixture ofsolvents. For example, if the total concentration of salt in the mixtureof solvents is 0.5 M, and the LiTFS concentration (in mole fraction) inthe mixture of solvents is 90 percent (i.e., 0.45 M), then the LiTFSIconcentration in the electrolyte mixture is ten percent (i.e., 0.05 M).In embodiments, other types of salts can be added to the electrolyte.

Other materials can be added to the electrolyte mixture. For example, incertain embodiments, electrochemical cell 10 includes an electrolyteformed of a mixture of solvents including EC, DME and PC, and a saltmixture of LiTFS and LiTFSI. The concentration of EC in the mixture ofsolvents can be from about five percent to about 30 percent by weight.The concentration of EC in the mixture of solvents can be equal to orgreater than five percent, ten percent, 15 percent, 20 percent, or 25percent by weight; and/or equal to or less than 30 percent, 25 percent,20 percent, 15 percent, or ten percent by weight. The concentration ofDME in the mixture of solvents can range from about 30 percent to about85 percent by weight. The concentration of DME in the mixture ofsolvents can be equal to or greater than 30 percent, 35 percent, 40percent, 45 percent, 50 percent, 55 percent, 60 percent, 65 percent, 70percent, 75 percent, or 80 percent by weight; and/or equal to or lessthan 85 percent, 80 percent, 75 percent, 70 percent, 65 percent, 60percent, 55 percent, 50 percent, 45 percent, 40 percent, or 35 percentby weight. The concentration of PC in the mixture of solvents can beequal to 100 percent minus the concentration of EC and DME. For example,if the concentration of EC in the mixture of solvents is 15 percent byweight, and the concentration of DME in the mixture of solvents is 60percent by weight, then the concentration of PC in the mixture ofsolvents is 25 percent by weight. Examples of an EC:DME:PC solventmixture are 14:62:24 and 10:75:15 percent by weight.

The LiTFS and LiTFSI concentrations in the electrolyte, e.g., from about0.4 M to about 1.2 M, can be generally similar to those describedherein. In embodiments, other types of salts can be added to theelectrolyte.

Cathode 16 includes an active cathode material, which is generallycoated on the cathode current collector. The current collector caninclude aluminum (e.g., in the form of an aluminum foil), an aluminumalloy, titanium, or nickel. In some embodiments, the current collectorcan be a metal grid. The current collector generally has at least onedimension (e.g., a length, a width, and/or a diameter) that is greaterthan about 0.2 millimeter (e.g., greater than about 0.5 millimeter,greater than about one millimeter, greater than about 1.5 millimeters,greater than about two millimeters). The active material can be, e.g., ametal oxide, halide, or chalcogenide; alternatively, the active materialcan be sulfur, an organosulfur polymer, or a conducting polymer.Specific examples include MnO₂, cobalt oxides, manganese spinels, V₂O₅,CoF₃, molybdenum-based materials such as MoS₂ and MoO₃, FeS₂, SOCl₂, S,and (C₆H₅N)_(n) and (S₃N₂)_(n), where n is at least two. The activematerial can also be a carbon monofluoride. An example is a compoundhaving the formula CF_(x), where x is from 0.5 to one, or higher. Theactive material can be mixed with a conductive material such as carbonand a binder such as polytetrafluoroethylene (PTFE) or Kraton (availablefrom Shell). An example of a cathode is one that includes aluminum foilcoated with MnO₂. The cathode can be prepared as described in U.S. Pat.No. 4,279,972. Specific cathode materials are a function of, e.g., thetype of cell (such as primary or secondary).

Anode 12 can include an active anode material, usually in the form of analkali metal (e.g., lithium, sodium, potassium) or an alkaline earthmetal (e.g., calcium, magnesium). The anode can include an alloy of analkali metal (e.g., lithium) and an alkaline earth metal or an alloy ofan alkali metal and aluminum. The anode can be used with or without asubstrate. The anode also can include an active anode material and abinder. In this case an active anode material can include tin-basedmaterials, carbon-based materials, such as carbon, graphite, anacetylenic mesophase carbon, coke, a metal oxide and/or a lithiatedmetal oxide. The binder can be, for example, PTFE. The active anodematerial and binder can be mixed to form a paste which can be applied tothe substrate of anode 12. Specific anode materials are a function of,for example, the type of cell (such as primary or secondary).

Separator 20 can be formed of any of the standard separator materialsused in electrochemical cells. For example, separator 20 can be formedof polypropylene (e.g., nonwoven polypropylene or microporouspolypropylene), polyethylene, a polysulfone, or combinations thereof.

Case 22 can be made of a metal (e.g., aluminum, an aluminum alloy,nickel, nickel plated steel) or a plastic (e.g., polyvinyl chloride,polypropylene, polysulfone, ABS or a polyamide).

Positive lead 18 and/or cap 24 can be made of, for example, aluminum,nickel, titanium, or steel.

Electrochemical cell 10 generally includes at least two metal or metalalloy surfaces that are in electrical contact with each other. As anexample, cathode 16 can include an aluminum current collector that is inelectrical contact with positive lead 18, which can be made of steel.The two metal surfaces that are in electrical contact with each othercan have the same composition (e.g., both surfaces can be made of thesame metal or metal alloy (e.g., both surfaces are made of aluminum)),or can have different compositions (e.g., the two surfaces can be madeof different metals or metal alloys (e.g., one surface is made ofaluminum and the other surface is made of an alloy of aluminum)). Asurface can have an interface between two portions having the samecomposition. The interface can have a different composition than theportions, e.g., due to wetting and diffusion.

While electrochemical cell 10 in FIG. 1 is a primary cell, in someembodiments a secondary cell can include one or more bis(oxalato)boratesalts. Primary electrochemical cells are meant to be discharged, e.g.,to exhaustion, only once, and then discarded. Primary cells are notintended to be recharged. Primary cells are described, for example, inDavid Linden, Handbook of Batteries (McGraw-Hill, 2d ed. 1995).Secondary electrochemical cells can be recharged for many times, e.g.,more than fifty times, more than a hundred times, or more. In somecases, secondary cells can include relatively robust separators, such asthose having many layers and/or that are relatively thick. Secondarycells can also be designed to accommodate for changes, such as swelling,that can occur in the cells. Secondary cells are described, e.g., inFalk & Salkind, “Alkaline Storage Batteries”, John Wiley & Sons, Inc.1969; U.S. Pat. No. 345,124; and French Patent No. 164,681, all herebyincorporated by reference.

To assemble the cell, separator 20 can be cut into pieces of a similarsize as anode 12 and cathode 16 and placed therebetween as shown inFIG. 1. Anode 12, cathode 16, and separator 20 are then placed withincase 22, which is then filled with the electrolytic solution and sealed.One end of case 22 is closed with cap 24 and annular insulating gasket26, which can provide a gas-tight and fluid-tight seal. Positive lead 18connects cathode 16 to cap 24. Safety valve 28 is disposed in the innerside of cap 24 and is configured to decrease the pressure withinelectrochemical cell 10 when the pressure exceeds some predeterminedvalue. Additional methods for assembling the cell are described in U.S.Pat. Nos. 4,279,972; 4,401,735; and 4,526,846.

Other configurations of electrochemical cell 10 can also be used,including, e.g., the coin cell configuration. The electrochemical cellscan be of different voltages, e.g., 1.5 V, 3.0 V, or 4.0 V.

The invention is further described in the following examples, which donot limit the scope of the invention described in the claims.

Example 1 Aluminum Corrosion at Different Voltages with Addition ofLithium-bis(oxalato)borate

Glass Cell Experimentation

An electrochemical glass cell was constructed having an aluminum workingelectrode, a lithium reference electrode, and two lithium auxiliaryelectrodes. The aluminum working electrode was fabricated from a 99.995%aluminum rod inserted into a Teflon sleeve to provide a planar electrodearea of 0.33 cm². The native oxide layer was removed by first polishingthe planar working surface with 600 grit aluminum oxide paper under anargon atmosphere, and cleaned in acetone in an ultrasonic bath.Thereafter, the aluminum electrode was thoroughly rinsed in electrolyte.The electrode was then immediately transferred into a glovebox for usein a three-electrode glass cell. All experiments were performed under anargon atmosphere.

Cyclic Voltammetry

Corrosion current measurements were made according to a modifiedprocedure generally described in X. Wang et al., Electrochemica Acta,vol. 45, pp. 2677-2684 (2000). The corrosion potential of aluminum wasdetermined by continuous cyclic voltammetry. In each cycle, thepotential was initially set to an open circuit potential, thenanodically scanned from +2.7 V to +4.5 V and reversed to an open circuitpotential. A scan rate of 50 mV/s was selected, at which goodreproducibility of the corrosion potential of aluminum was obtained. Thecorrosion potential of aluminum was defined as the potential at whichthe anodic current density reached 10⁻⁵ A/cm² at the first cycle. Thecurrent was recorded as a function of voltage.

Chronoamperometry

Corrosion current measurements were made according to the proceduredescribed in EP 0 852 072. The aluminum electrode was polarized atvarious potentials between 3.6 V and 4.5 V versus a lithium referenceelectrode while the current was recorded versus time. Current versustime measurements were taken over a 30-minute period. The area under thecurrent versus time curve was used as a measure of the amount ofaluminum corrosion occurring. The experiment also could be terminated incase the current density reached three mA/cm² before the 30-minute timeperiod elapsed and no corrosion suppression occurred. Corrosionsuppression occurred when the resulting current density was observed inthe range of 10⁻⁶ A/cm².

Referring to FIG. 2, curves “a” and “b” show the potentiostaticdependence (chronoamperograms) of an aluminum electrode exposed atdifferent voltages to an electrolyte containing 12.6% ethylenecarbonate, 25.3% propylene carbonate, 62.1% dimethoxyethane, 0.64 MLiTFS, and 0.01 M lithium-bis(oxalato)borate. Curve “a” shows achronoamperogram of the aluminum electrode at +3.6 V, while curve “b”shows a chronoamperogram of the aluminum electrode at +3.8 V. As shownin FIG. 2, at a lithium-bis(oxalato)borate concentration of 0.01 M,aluminum corrosion at +3.6 V (versus a lithium reference electrode) waseffectively suppressed (i.e., the corrosion current at +3.6 V was around10 μA/cm²). Aluminum corrosion did take place, however, in the sameconcentration of lithium-bis(oxalato)borate (i.e., 0.01 M) at +3.8 V(versus a lithium reference electrode).

Referring to FIG. 3, curves “a”, “b”, “c”, and “d” show thepotentiostatic dependence (chronoamperograms) of an aluminum electrodeexposed at different voltages to an electrolyte containing 12.6%ethylene carbonate, 25.3% propylene carbonate, 62.1% dimethoxyethane,0.64 M LiTFS, and 0.03 M lithium-bis(oxalato)borate. Curve “a” shows achronoamperogram of the aluminum electrode at +3.6 V; curve “b” shows achronoamperogram of the aluminum electrode at +3.8 V; curve “c” shows achronoamperogram of the aluminum electrode at +4.0 V; and curve “d”shows a chronoamperogram of the aluminum electrode at +4.2 V. As shownin FIG. 3, at a lithium-bis(oxalato)borate concentration of 0.03 M,aluminum corrosion at +3.6 V (versus a lithium reference electrode)decreased to 3.5 μA/cm². Thus, the addition of morelithium-bis(oxalato)borate to the electrolyte helped to further suppressaluminum corrosion at +3.6 V.

Referring to FIG. 4, curves “a”, “b”, “c”, and “d” show thepotentiostatic dependence (chronoamperograms) of an aluminum electrodeexposed at different voltages to an electrolyte containing 12.6%ethylene carbonate, 25.3% propylene carbonate, 62.1% dimethoxyethane,0.64 M LiTFS, and 0.05 M lithium-bis(oxalato)borate. Curve “a” shows achronoamperogram of the aluminum electrode at +3.8 V; curve “b” shows achronoamperogram of the aluminum electrode at +4.0 V; curve “c” shows achronoamperogram of the aluminum electrode at +4.2 V; and curve “d”shows a chronoamperogram of the aluminum electrode at +4.5 V. As shownin FIG. 4, at a lithium-bis(oxalato)borate concentration of 0.05 M,aluminum corrosion was effectively suppressed up to +4.0 V (versus alithium reference electrode). With the addition to the electrolyte oflithium-bis(oxalato)borate at a concentration of 0.05 M, the corrosioncurrent at +3.8 V and at +4.0 V was from about one μA/cm² to about twoμA/cm². Thus, the addition of more lithium-bis(oxalato)borate to theelectrolyte helped to further suppress aluminum corrosion at +3.8 V andat +4.0 V.

Referring to FIG. 5, curves “a”, “b”, “c”, and “d” show thepotentiostatic dependence (chronoamperograms) of an aluminum electrodeexposed at different voltages to an electrolyte containing 12.6%ethylene carbonate, 25.3% propylene carbonate, 62.1% dimethoxyethane,0.64 M LiTFS, and 0.1 M lithium-bis(oxalato)borate. Curve “a” shows achronoamperogram of the aluminum electrode at +3.8 V; curve “b” shows achronoamperogram of the aluminum electrode at +4.0 V; curve “c” shows achronoamperogram of the aluminum electrode at +4.2 V; and curve “d”shows a chronoamperogram of the aluminum electrode at +4.5 V. As shownin FIG. 5, at a lithium-bis(oxalato)borate concentration of 0.1 M, thealuminum electrode was stable in the electrolyte up to +4.2 V (versus alithium reference electrode). With the addition to the electrolyte oflithium-bis(oxalato)borate at a concentration of 0.1 M, the corrosioncurrent at +4.2 V was about 3.5 μA/cm². Thus, the addition of morelithium-bis(oxalato)borate to the electrolyte helped to further suppressaluminum corrosion at +4.2 V.

Referring to FIG. 6, cyclic voltammograms taken in the electrolytecontaining 12.6% ethylene carbonate, 25.3% propylene carbonate, 62.1%dimethoxyethane, 0.64M LiTFS, and different concentrations oflithium-bis(oxalato)borate showed significant shifts in the corrosionpotential of the aluminum electrode. The addition oflithium-bis(oxalato)borate to the electrolyte shifted the potential ofaluminum in the positive direction, which indicates corrosionsuppression. Curve “a” in FIG. 6 shows the corrosion potential of thealuminum in an electrolyte containing no lithium-bis(oxalato)borate. Theaddition of lithium-bis(oxalato)borate to the electrolyte at aconcentration of 0.03 M shifted the corrosion potential of the aluminumabout 800 mV in the positive direction (curve “b”). With the addition oflithium-bis(oxalato)borate to the electrolyte at concentrations of 0.05M (curve “c”), 0.1 M (curve “d”) and 0.2 M (curve “e”), the corrosionpotential of the aluminum was shifted to around 4.1 V. These resultsdemonstrate that the addition of increasing amounts oflithium-bis(oxalato)borate to the electrolyte containing 12.6% ethylenecarbonate, 25.3% propylene carbonate, 62.1% dimethoxyethane, and 0.64 MLiTFS results in increasing degrees of corrosion protection of thealuminum electrode up to about 4.1 V.

All publications, patents, and patent applications referred to in thisapplication are herein incorporated by reference to the same extent asif each individual publication, patent, or patent application wasspecifically and individually indicated to be incorporated by reference.

Other embodiments are possible. For example, although the examplesdescribed above relate to batteries, the invention can be used tosuppress aluminum corrosion in systems other than batteries, in which analuminum-metal couple occurs.

Other embodiments are within the claims.

What is claimed is:
 1. An electrochemical cell comprising: a cathodecontaining an aluminum current collector; a positive lead including ametal selected from the group consisting of aluminum, titanium, andsteel coupled to the aluminum current collector; an anode comprising amaterial selected from the group consisting of lithium, graphite, and alithiated metal oxide; and an electrolyte containing (1) from greaterthan 0.075 M to less than 0.2 M of a bis(oxalato)borate salt selectedfrom the group consisting of metal bis(oxalate)borate salts and ammoniumbis(oxalato)borate salts, and (2) a second salt comprising a lithiumsalt, and wherein the aluminum current collector has an aluminum surfacehaving at least one dimension greater than 1 millimeter.
 2. Theelectrochemical cell of claim 1, wherein the bis(oxalato)borate salt islithium bis(oxalato)borate.
 3. The electrochemical cell of claim 1,wherein the second salt is lithium trifluoromethanesulfonate.
 4. Theelectrochemical cell of claim 1, wherein the positive lead comprisessteel.
 5. An electrochemical cell comprising: a cathode containing acurrent collector comprising a first aluminum alloy; a positive leadcomprising a second aluminum alloy different from the first aluminumalloy coupled to the current collector; an anode comprising a materialselected from the group consisting of lithium, graphite, and a lithiatedmetal oxide; and an electrolyte containing from greater than 0.075 M toless than 0.2 M of a bis(oxalato)borate salt and a second saltcomprising a lithium salt; and wherein the cathode current collector hasan aluminum surface having at least one dimension greater than 1millimeter.
 6. The electrochemical cell of claim 5, wherein thebis(oxalato)borate salt is lithium bis(oxalato)borate.
 7. Theelectrochemical cell of claim 5, wherein the electrolyte furthercontains lithium trifluoromethanesulfonate.